The invention concerns a process for the control or regulation of at least two process entities, wherein a parameter of one of the two process entities is measured and compared with a reference value, and wherein the second process value becomes larger than the first process value if the measured value exceeds the reference value.
In process technology it is frequently necessary to chose between two process entities, for example, to switch for cooling purposes from a warmer liquid to a colder liquid. Such switching procedures lead to an unsteadiness of the process; in the example cited, they cause undesirable temperature jumps.
It is the object of the invention to reduce the unsteadiness appearing upon switching between different process entities.
This object is attained in that the first process entity is maintained constant and the second process entity is increased by a rising measured value, if the measured value is smaller than the reference value but larger than a given lower value; and the second process entity is maintained constant and the first process entity is reduced by a rising, measured value, if the measured value is larger than the reference value, but smaller than a given upper value.
In the afore-mentioned example, the volume flowing through of the warmer liquid is increased with decreasing differences between the temperature of the warmer liquid and the colder liquid. If the temperature of the formerly colder liquid exceeds the temperature of the formerly warmer liquid, the volume flowing through of the formerly colder liquid is decreased with increasing differential between the two temperatures. In this manner, a transition from one process entity to the other process entity, i.e., a replacement of one cooling liquid by the other is obtained in which only a slight unsteadiness of the cooling temperature occurs.
In the present invention a parameter of the other process entity is measured as the given value. It is convenient to measure the same parameter of the individual process entities. It is possible in this manner to take into consideration any potential parameter variations of the two entities. In the afore-mentioned example, the temperatures of the two liquids are measured and the colder liquid selected for cooling.
It is further advantageous if the variation of one process entity is a function of at least one measured value. The manner in which a process entity is increased or reduced is thus effected as a function of one parameter of the process entities. In the example mentioned, the warming cooling liquid is reduced linearly, e.g., its temperature is higher than that of the other liquid. The rise in the linear reduction depends on the difference of the temperatures of the two liquids.